The GDNF (Glial cell line-derived neurotrophic factor)/Ret/Akt signaling pathway is essential to the development of ENS (enteric nervous system) as well as kidney. We previously showed that the HECT-type E3 ligase NEDL2 (Nedd4-like ligase 2) is required for the ENS development by activating GDNF/Ret/Akt. However, the underlying mechanism remains unknown. Here we show that in addition to ENS, NEDL2 is also pivotal for kidney development since about 1/3 of Nedl2-deficient mice displayed postnatal unilateral or bilateral kidney hydronephrosis. Double knockout of Nedl1 and Nedl2 in mice leads to postnatal lethal within 2 weeks and the phenotypes resemble those of Nedl2 single knockout mice. Surprisingly, its close member NEDL1 is dispensable for ENS and kidney function and the reason is lack of NEDL1 expression in these systems during early development. Furthermore, biochemical analysis indicated that NEDL2 appears to act like a scaffold protein to recruit SHC, Grb2, PI3K (p110 and p85), PDK1 and Akt together to promote the signaling transduction. Intriguingly, we found that NEDL2 harbours intrinsic Nedd8 ligase activity with cysteine 1341 as the core site. NEDL2 upregulates GDNF-stimulated Akt activity dependent of its Nedd8 ligase activity but not its ubiquitin ligase activity. These findings demonstrate that NEDL2 but not NEDL1 is required for ENS and kidney development in a unique Nedd8 ligase-dependent manner.
Keywords: GDNF/Ret/Akt pathway; Nedd8 ligase; kidney development; scaffold protein; ubiquitin ligase.